This invention relates to new polyisocyanate preparations containing latent tin catalysts, a process for preparing these new polyisocyanate preparations and a process for the production of polyurethane plastics from these polyisocyanate preparations.
The catalysis of isocyanate addition reactions plays an important part in technical polyurethane chemistry such as the production of polyurethane foams, elastomers, lacquers and adhesives.
Tertiary amines and especially organic tin compounds are catalysts used for this purpose. These compounds catalyze urethanization (reaction of isocyanate groups with alcoholic hydroxyl groups) and urea formation (reaction of isocyanate groups with water) as well as the trimerization of isocyanate groups, addition of isocyanate groups to urethane groups (allophanatization) and addition of isocyanate groups to urea groups (biuretization).
Organic tin compounds are particularly valuable catalysts used in both one component and two component polyurethane systems. A survey of the catalysts commonly used and the mechanism of their action may be found in A. Farkas and G. A. Mills, Advan. Catalysis, 13, 393 (1962), J. H. Saunders and K. C. Frisch, Polyurethanes, Part I, Wiley Interscience, New York, 1962, Chapter VI, and K. C. Frisch and L. P. Rumao, J. Macromol, Sci. Revs. Macromol Chem., C5(1), 103-150 (1970).
However, catalytically active tin compounds, in particular tin carboxylates and tin alkoxides have two serious disadvantages.
First, these active tin compounds are sensitive to hydrolysis. Therefore, they cannot readily be incorporated in the usual polyol formulations, which generally contain traces of moisture because they would gradually lose some of their catalytic activity when stored in the polyol formulations.
The second disadvantage of these active tin compounds is that when they are used for organic polyisocyanates (i.e. the polyisocyanate component of 2-component systems or isocyanate prepolymers of the kind used as binders in one component systems such as moisture drying coating compounds), they should be incorporated only shortly before the systems are applied because their presence would seriously impair the storage stability of the polyisocyanates due to the above-mentioned side reactions which are catalyzed by tin compounds.